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I ordered some TDAs.  At this stage as it is impossible to trace where the problem is so removed every semiconductor on the board and will get them tested on a curve tracer.  If none of the fail I will mode to inductors, then ceramics, then resistors.  I will put it completely apart till I...

Dp3 and Dp4 signal diodes are fine on mine. Reverse biased up to 100vdc and no leak. CNY17 is also good.  I think my culprit is the signal out of IP1 pin 5.  Any other ideas?

They are there but do not align. If I adjust the POT I cannot get them all balanced. Find the +12 has a bit of a ripple. I did test Dp11, Dp5, Dp7, Dp4, Dp8, Dp12, Dp2 on a good curve tracer and they are good.  The feedback Mosfet seems ok under basic testing. Haven't got it to the curve...

I have replaced some leaky capacitors on the analog and digital board of this mac. I did check some of the key voltages on the switching power supply block that seems to be inline with that Bomarc schematic.  One test I did was to disconnect the +5 and +/-12 lines from the analog board and...

Is it possible to duplicate the Mac OS system 6 OS disk using the Mac Plus itself to do it?  Will DiskCopy 4.2 be able to do it?

Did a few more probing. Lifted R30 to isolate pin #20 (Video out) of BMU2 from the analog board and everything else. Nothing is damping it... it is pretty much weak on it's own. Also did some logic probing on the BMU2. All Is and I/Os are pulsing apart from I14 as it is nodded to OE.  Would...

Anyone out there with an open Mac Plus who could send an oscilloscope plot of J8 pins 1, 3 and 5? Specially pin 1 which is video out. Probing it I just got a noisy LOW signal. I was suspicious of my LAG IC but after probing V & H sync I got clear pulses at 60HZ & 22KHZ which seems to...

Yes me too. I am reluctant to go and buy a logic board without covering all possible issues with the analog board.  All books mention about replacing U2 but none mention which gate of U2 controls the horizontal signal. If I knew that I could trace all between U2 and CRT and see if I find something.

Just found it!

I know what could be then... I am reading the Mac Plus logic is grounded to chassis and I discharged the CRT to chassis without a resistor. Apparently the logic board is sensible to that. Makes no sense to be the analog as I replaced the ICs and tested all transistors. Are you able to show me...

No silly question. Any comment is welcome. That is a tricky one. Wish I had schematics with voltages and waveforms to test against. If the brightness you refer if the one in the front under the screen. It works as intended as brightness control. But messing with it does not remove the...

Could be but I have redone all the joints on the analog board. Fluxed and added a bit of new solder. Unlikely it is that. I will check continuity on all cables and see if I find anything.

Did some more extensive checks. Replaced the LS38. Checked most of the transistors around the LS38 and nothing. Still the same issue. Also re-soldered the large connector on the logic board just to make sure. Nothing. Any ideas?! Other things to try?

I just replaced the LS38 logic and nothing. Still the same issue. will try page 169 as may be a transistor.... keep you posted!

Hi   I bought one of these and can really get it to read or format a 720k/800k disk on my mac.    I am running mac os Mojave.    Is there anything I am doing wrong?   Cheers, Gui

Thanks mate! I was trying to figure out what was this DMS thing... thanks for the tip. Amazing book! It is pretty much it. I did test the 7438 and all gates seem fine. I ordered a new one anyway. Lets see if that is it.

I am struggling a bit to identify this fault. The computer beeps once and reads the system disk apparently fine but the only image I get is the attached one.  See image attached. Following the manual I found here on the forum seems my voltages seem ok. I did read on a post yesterday...

Hi, I got the same issue on my Plus.  Would you be able to let me know what is the DMS you are looking at? Or where I could download it? Cheers!